The present invention relates to a joining device for rigidly locking two complementary joining parts together of which at least a first part is made of molded plastic, comprising a female part joined to said first joining part by molding it at the same time as said first joining part and a male part joined to the second joining part.
For several decades the housings of electronic devices, at least as regards small and medium-sized devices, have more often than not been formed by two plastic joining parts joined together. At the beginning the assembling was carried out, in essence, with screws, in continuation of what is commonly done for metallic housings. Gradually, progress has been made in the molding of joining parts of plastic and it has become possible to put at least partly the joining parts together by clipping complementary parts that fit together in both joining parts, these parts being obtained by molding them at the same time as their joining part and their coupling being realized by under-pressure, by means of a previous deformation that is permitted because of the elasticity of the plastic material.
A medium-sized device is notably understood to mean television receivers, various elements of an audio or video set or of a personal computer, a telephone base station, and a small device is understood to mean a pocket calculator, an infrared remote control and, more recently, a cellular or cordless telephone handset.
Screwing the joining parts onto each other provides the advantage of a proper assembly strength and is a guarantee that joining parts will not come loose during a shock notably due to a fall, this being certainly true for small electronic devices which are autonomous because they have a battery and are handheld.
Alternatively, joining two joining parts firmly together with screws has several drawbacks too: it implies the supply of separate elements, that is to say, screws, and a rather long assembly time which is directly proportional to the number of screws provided, more often than not more than 4, so that the result is rather high assembly costs and also a drawback that is less apparent than the two preceding ones but perhaps paramount, which is the fact that it is all too easy to separate the two parts, notably by a private person, which may invalidate the effect of guarantee of the device in case it breaks down.
The balance of reciprocal advantages and disadvantages of the screwing and clipping generally results in a compromise which consists of clipping the main part and retaining at least one screw to achieve this joining together.
Nowadays, however, one wishes to join the joining parts together entirely by clipping including small devices which, more than minimum-sized devices, are liable to drops.
With the conventional type of clipping as described, for example, in U.S. Pat. No. 5,536,917 particularly with reference to FIG. 1 of this patent specification, each joining device intended to replace a screw is formed by a male part on one joining part and a female part on the other joining part, with a sufficiently narrow protrusion on each joining part and the catch that is realized is simple in the sense that it needs a single face of each coupling during assembly. Under these conditions and if the device drops, the joining parts are twisted in diverging directions to the point where in their relative movements they take along the joining parts which they comprise and which they come uncouple. The joining parts may also be broken as a consequence of the shock. Furthermore, the molding operations of the joining parts have become ever more precise, permitting small thicknesses (of the order of 2 mm) which intensifies their deformation in case of shocks. To remedy this, while maintaining the type of clipping of the afore-mentioned type, the joining devices may be reinforced by increasing their dimensions, particularly their thickness and also their number. This reduces the risk of breakage and coming loose during a fall, but this does not resolve the technical problem as regards the screwing that may be entirely omitted and thus also brings about a new problem for persons who have to realize the assembly manually: the reinforcement of the joining devices requires a pressure which is accordingly higher, which pressure becomes inadmissible beyond a certain threshold.
It is an object of the invention to realize a rapid assembly of two plastic joining parts which form the housing of an electronic device by totally or partly doing away with the assembly with screws.
It is another object of the invention to realize the assembly of two plastic joining parts by means of joining devices realized by molding at the same time as the joining parts and in such a way that these joining parts will not come loose in case they drop.
A still further object of the invention is to realize the assembly of two fully plastic joining parts by means of joining devices realized by molding at the same time as the joining parts and in such a way that the forces required for the assembly remain in a range of quite low values.
These objects are achieved and the drawbacks of the prior art are mitigated thanks to the fact that a joining device described in the opening paragraph is characterized in that said female part is formed by at least two hooks positioned symmetrically opposite one another so as to determine between them in longitudinal direction two spaces into which the male part is to be pushed, a first inserting space of a flared shape, said flare having its large diameter at the free end and a second space of rectangular longitudinal section called retaining space, the interface between said first and second space forming at least two female shoulders for said hooks, and in that the complementary male part situated opposite has an inserting end which has a slightly smaller diameter than the large diameter of said flare and then becomes larger until a common shoulder of the male part is reached.
The symmetry thus brought to each of the two parts of each joining device and their independent concept of the walls of the joining parts prevents this joining device from coming loose. In effect, if during a shock the two parts have a tendency to come loose on one side of the joining device, the retaining effect is reinforced accordingly on the opposite side and after the shock the two sides remain firmly attached together. It will be noted that the increased reliability for attaching the joining parts together is important for small devices which are intended to be held in hand and are thus more exposed to drops than medium-sized devices. Moreover, the small devices such as a mobile telephone handset are designed for resisting shocks and are to continue operation even after various drops. All the more reasons for the housing of the device not be dislocated after the fall, even a quite violent fall.
A preferred embodiment of the invention is characterized in that said female part is formed by a clip having two symmetrical hooks relative to a plane of symmetry and in that said male part which stretches out in said plane of symmetry perpendicularly to the longitudinal direction of said hooks, has a section whose shape is constituted by an arc of circle as regards its inserting part and by two slightly retractable planes which form said common shoulder of the male part relative to its opposite part which is complementary to its inserting part.
This embodiment is quite interesting for small devices because it lends itself well to a miniaturization. For that matter, small devices, mostly mobiles, include a battery and it is convenient to put such joining devices into a part whose volume is occupied by the battery, which permits the access to these housings in case they are to be taken apart.
A further preferred embodiment of the invention is characterized in that said female part is formed by a substantially cylindrical sleeve and comprises at least three hooks separated by longitudinal grooves, said first space forming a truncate cone and said second space a cylinder and in that the male part is formed by a dog joint with a cone-shaped end.
This further preferred embodiment of the invention is highly suitable for medium-sized devices where the miniaturization is not the first concern. Furthermore, it permits of unlocking joining devices from the outside of the device and this by means of a tool designed for this purpose which does not form part of the present invention.
It will be noted that for the two embodiments described before, the male part of the joining device is solid and may deform only slightly. This makes it possible to join two joining parts together of which one, made of plastic, preferably of ABS, comprises the female parts of the joining devices and the other may be metallic and comprise complementary male parts made of metal.